1. Field of the Invention
The present invention relates to duckbill conservation vent valves utilized to control the direction of fluid flow.
2. Description of Related Art
Duckbill valves are used in a wide variety of situations to prevent the reversal of direction of fluid flow. U.S. Pat. No. 4,524,805 to Hoffman discloses a duckbill valve for controlling the direction of fluid flow in a fluid-conducting conduit. The valve is formed of elastomeric material and comprises a generally axial fluid passageway having an inlet and an outlet end provided with an outlet slit. The valve is progressively narrowing in cross sections from the inlet end to the outlet end to define a pair of opposed sealing lips at the outlet slit. Means for urging the sealing lips closed are comprised of widened lip margins at opposite ends of the outlet slit. The valve is formed by molding the elastomeric material into the preferred shape and then providing the widened lip margins with a closing bias by causing a greater amount of shrinkage in the lip margins, relative to the remaining portions of the sealing lips, during curing of the molded material from an elevated curing temperature to room temperature. Once Hoffman's valve is made, no way exists to vary the strength of the means for urging the sealing lips closed to adapt the valve to changing conditions. Therefore, a need exists for a valve on which the closure force on the valve lips can be varied after the valve body has been constructed to thereby allow the valve user to vary valve lip closure strength as conditions necessitate.
U.S. Pat. No. 3,465,595 to Tansony discloses a liquid sampling device including a submersible container for receiving samples of liquid from a bath thereof for transmission to a testing station external to the bath. The sampler has a duckbill-shaped hose inlet for the liquid functioning as a one-way check valve and also as a screen to prevent entry of undesirable lumps of solids into the container. The duckbill-shaped hose inlet of Tansony's patent prevents lumps of solids from entering the container, but is not disclosed as being capable of functioning as a conservation vent valve, capable of opening at pressures of less than 2 inches of water.
U.S. Pat. Nos. 4,585,031 and 4,607,663 to Raftis and Merritt disclose tide gate valves for large sized conduits which resist inversion and sagging and which open easily. These valves comprise a sleeve bounding a longitudinally extending flow-through passage for fluids. The sleeve has an upstream fluid inlet end region mountable on a discharge end of a conduit which is elongated along an axis of symmetry. The sleeve also has a downstream fluid outlet end region which has an upper lip and a lower lip opposed to each other relative to the axis. The lips are movable from a closed position in which the lips engage each other, to an open position in which the lips are located apart from each other in response to a pressure head within the passage and exerted in a direction downstream of the passage. The sleeve further has a tapered intermediate region. The upper and lower walls respectively merge, and are jointly movable, with the upper and lower lips. The sleeve is constituted, at least in part, of a flexible material and has pads or plies to provide support to the lips to prevent sagging and inversion due to back pressure. Both tide gate valves are suited primarily for prevention of fluid backflow in storm or sanitary sewage lines. Neither tide gate valve is suitable as a conservation vent valve capable of opening at pressure heads of 2 inches of water or less. Thus a need exists for a duck-billed conservation vent valve which is capable of opening at pressure heads of 2 inches of water or less.
Accordingly, it is an object of the present invention to provide a duck-billed conservation valve in which the closure force on the valve lips can be varied after the valve body has been constructed and which is opened at pressure heads of 2 inches of water or less.